1. Singularities of Caustics and Wave Fronts;Arnol'd,1990
2. Singularities of Differentiable Maps, vol. I;Arnol'd,1986
3. What is an envelope?;Bruce;Math. Gaz.,1981
4. Curves and Singularities. A Geometrical Introduction to Singularity Theory;Bruce,1992
5. Caustics through the looking glass;Bruce;Math. Intelligencer,1984